Petroleum-derived solvents and fuels are of environmental concern and are under legislation to be replaced by biorenewable substitutes that afford reduced environmental impact. Unpredictable petroleum prices and the increasing desire for energy independence and security have led to burgeoning research activities directed toward developing a variety of alternative fuels. Among these new fuels, biodiesel is a biorenewable, nontoxic diesel that can be produced by transesterification of various oil feedstocks, including vegetable oils, animal fats, algal oils, and restaurant waste oils. Examples of biodiesel can include fatty acid C1-5 alkyl esters, such as soy diesel (methyl soyate), rapeseed methyl ester, and various vegetable and animal fat methyl esters. Another new fuel is green diesel or renewable diesel, produced by hydrotreatment of various oils to produce a hydrocarbon mixture. Green diesel can be chemically identical to petroleum-derived fuels.
Catalysts are essential materials in a wide variety of useful and important chemical reactions, such as hydrotreatment. Many catalysts lack selectivity Generally, catalysts are unselectively exposed to materials in a chemical reaction. Therefore, a molecule at lower concentration with a particular reactivity with the catalyst has a lower chance of undergoing the chemical change caused by the catalyst than a different molecule at a higher concentration having the same reactivity with the catalyst.